JP4588606B2 - Belt drive control device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a belt drive control device that controls the rotation of a driving support rotating body to which a rotational driving force is transmitted among a plurality of supporting rotating bodies on which an endless belt is stretched, and a copier, printer, and facsimile using the same. And the like.

Conventionally, in an electrophotographic image forming apparatus, when an endless belt such as a photosensitive belt as an image carrier, an intermediate transfer belt, or a paper conveying belt as a recording material conveying member is used, the belt is driven with high accuracy. Control is essential to obtain high quality images. In particular, in a tandem type color image forming apparatus excellent in image forming speed and suitable for downsizing, an intermediate transfer belt and a recording sheet on which images of respective colors formed on a plurality of latent image carriers are transferred so as to overlap each other are used. Highly accurate drive control of the paper transport belt to be transported is required.
Here, an example of a tandem type color image forming apparatus that transfers images of respective colors formed on a plurality of latent image carriers onto a recording sheet so as to overlap each other will be specifically described. In this tandem type color image forming apparatus, for example, image forming units that form monochrome images of yellow, magenta, cyan, and black are sequentially arranged in the conveyance direction of the recording paper. Then, the electrostatic latent image formed on the surface of the photoreceptor, which is a latent image carrier, is developed by each image forming unit by the laser exposure unit, thereby forming a toner image. The toner images of the respective colors are sequentially superimposed and transferred onto the recording paper that is attached to the paper conveyance belt and conveyed by electrostatic force, and then the toner is melted and pressure-bonded by a fixing device, so that the color is printed on the recording paper. An image is formed. The paper transport belt is stretched with an appropriate tension between a driving roller (driving support rotator) and a driven roller (driven supporting rotator) arranged in parallel to each other. The drive roller is rotationally driven at a predetermined rotational speed by a motor (drive source), and the paper transport belt is also rotationally moved at a predetermined speed. The recording paper is supplied to the image forming unit side of the paper transport belt at a predetermined timing by the paper feed mechanism, and is moved and transported at the same speed as the moving speed of the paper transport belt, thereby sequentially passing through each image forming unit. . In such a tandem type color image forming apparatus, maintaining the conveyance speed of the recording paper, that is, the movement speed of the conveyance belt, at a predetermined speed reduces the relative positional deviation of the monochromatic images superimposed on the recording paper. It is extremely important in making it happen.

In order to realize high-precision drive control of the belt, conventionally, a drive control method for controlling the rotation of the drive roller so as to make the rotation speed of the drive roller driving the belt constant is known. In this drive control method, the rotational speed of the driving roller is made constant by maintaining the rotational angular speed of the motor that is the driving source and the rotational angular speed of the gear that transmits the rotational driving force generated by the motor to the driving roller. This is a drive control method. However, this drive control method makes the belt moving speed constant even if the rotational angular velocity of the driving roller is constant when the belt thickness varies, particularly when there is a thickness variation along the belt moving direction (belt circumferential direction). There was a bug that it was not possible.
More specifically, when the belt is driven by the driving roller, the inner circumferential surface side of the belt tends to move at the same speed as the outer circumferential surface of the driving roller, and tends to move at a faster speed toward the outer circumferential surface side of the belt. The entire belt is driven at the moving speed at the center in the belt thickness direction. Here, when the thickness varies in the circumferential direction of the belt, the distance between the inner circumferential surface of the belt and the central portion in the belt thickness direction (hereinafter referred to as “effective belt thickness” serving as a reference for the moving speed) also varies. For this reason, even if the rotational angular velocity of the driving roller is constant, the moving speed of the belt driven by the driving roller varies due to a change in the thickness of the belt portion in contact with the driving roller. Specifically, if the belt portion in contact with the driving roller is a thick portion, the belt moving speed is high, and if the belt portion is a thin portion, the belt moving speed is low.

Therefore, the present applicant has proposed a belt drive control method that can eliminate this problem (Patent Document 1). Hereinafter, the belt drive control method proposed in Patent Document 1 will be described.
When the driven roller rotates following the movement of the belt, the driven roller rotates so that the outer peripheral surface moves at the same speed as the inner peripheral surface of the belt. The inner peripheral surface of the belt, that is, the outer peripheral surface of the driven roller moves slower than the moving speed of the entire belt (moving speed at the center in the belt thickness direction). For this reason, even if the moving speed of the entire belt is constant, the rotational angular speed of the driven roller varies depending on the thickness of the belt portion in contact with the driven roller. For example, when the thick belt portion is in contact with the driven roller, the rotation of the driven roller is slow, and when the thin belt portion is in contact with the driven roller, the rotation of the driven roller is fast. Thus, the rotation of the driven roller varies according to the thickness of the belt.
In the belt drive control method proposed in Patent Document 1, the following drive control is performed using the rotational fluctuation of the driven roller in accordance with the thickness of the belt. That is, the rotational angular displacement or rotational angular velocity of the driven roller is detected, and from the detected data, the rotational angular velocity of the driven roller having a frequency corresponding to the periodic thickness variation (belt thickness variation) in the circumferential direction of the belt. Extract AC components. The amplitude and phase of the extracted alternating current component correspond to the amplitude and phase of the belt thickness variation. Therefore, the amplitude and phase of the belt thickness fluctuation can be grasped from the amplitude and phase of the AC component. In the belt drive control method proposed in Patent Document 1, based on the amplitude and phase of the alternating current component, the rotational angular velocity of the drive roller is lowered at the timing when the thick belt portion contacts the drive roller, and conversely the drive roller When the thin belt portion is in contact, control is performed to increase the rotational angular velocity of the drive roller. By repeating this control, according to the belt drive control method proposed in Patent Document 1, the belt is driven at a constant moving speed without being affected by the belt thickness fluctuation in consideration of the belt thickness fluctuation. Can do.

JP 2004-123383 A

However, as a result of research by the present inventors, even if the belt is driven using a belt drive control method that takes into account fluctuations in the belt thickness, such as the belt drive control method proposed in Patent Document 1, the belt remains constant. It became clear that there was a case that it could not be driven at the moving speed.
More specifically, it has been confirmed that if the belt is left in a tensioned state after the belt driving is stopped, the belt thickness at a specific point on the belt moving path changes. In the example confirmed by the present inventors, the belt to be driven and controlled is an elastic belt, and the thickness of the belt portion at the place where the entrance roller 61 is wound (a specific point) is left in the belt spanning configuration shown in FIG. Became thicker. In addition, the thickness of the belt portion at a specific point between the two rollers 62 and 63 was reduced by standing. If the belt thickness at a specific point on the belt moving path changes by leaving the belt in this way, the amplitude and phase of the belt thickness fluctuation after being left are changed from those before being left. As a result, the belt moving speed after being left unattended cannot be made constant even if belt drive control is performed based on the change in belt thickness obtained before being left unattended.

  Further, in the belt drive control method proposed in Patent Document 1, the rotational angular displacement or rotational angular velocity of the driven roller is detected, and the belt thickness variation is grasped from the detected data. Therefore, it is possible to keep the moving speed of the belt after being left constant if the belt thickness fluctuation is re-recognized every time the belt is left and the belt drive control is performed based on the newly recognized belt thickness fluctuation. . In Patent Document 1, a low-pass filter and a bandpass for extracting an AC component having a frequency corresponding to a belt thickness variation from detected data as a configuration capable of re-recognizing the belt thickness variation every time it is left unattended. The fact that a filter is used is described. However, in general, the period of belt thickness fluctuation corresponds to the time for the belt to make one revolution, and the frequency of belt thickness fluctuation is 1 Hz or less. Since it is difficult to realize a filter that separates such a low frequency, an increase in cost is inevitable for realizing such a filter.

  The present invention has been made in view of the above background, and the object of the present invention is to provide a belt that has been left unattended at a low cost even when the belt thickness at a specific point on the belt moving path changes due to the unattended. A belt drive control device that can be driven at a moving speed and an image forming apparatus using the belt drive control device.

In order to achieve the above-mentioned object, the invention of claim 1 is for canceling fluctuations in belt moving speed due to periodic belt thickness fluctuations in the circumferential direction of an endless belt stretched over a plurality of support rotating bodies. Based on the target value storage means for storing the target value data and the target value data stored in the target value storage means, the rotation of the driving support rotator to which the rotational driving force is transmitted among the plurality of support rotators. A rotation control means for controlling, a stop position detecting means for detecting a stop position of the belt when the belt is stopped, a time measuring means for measuring a standing time from the stop of driving of the belt to the start of the next drive, Based on the stop position detected by the stop position detecting means, the belt portion located at a specific point where the thickness of the belt changes is specified by leaving the belt in a driving stop state; and Based on the measurement result of the time measurement means, the target value storage means stores the target value data corresponding to the belt thickness variation after the belt thickness change of the belt portion due to the neglected time for the measurement result. And target value correcting means for correcting the target value data.
According to a second aspect of the present invention, in the belt drive control device according to the first aspect, the target value correcting means is based on the stop position detected by the stop position detecting means, and the phase is changed according to the stop position. The target value data stored in the target value storage means is corrected so that the target value data corresponding to the belt thickness fluctuation is corrected.
According to a third aspect of the present invention, in the belt drive control device according to the first aspect, the rotation control means controls the belt to stop at a predetermined reference stop position when stopping the driving of the belt. It is characterized by doing.
According to a fourth aspect of the present invention, there is provided the belt drive control device according to the third aspect, wherein the reference stop position is at a specific point where the thickness of the belt changes when the belt is left in the drive stop state. It is a position where the thickest belt portion or the thinnest belt portion stops in the belt circumferential direction.
According to a fifth aspect of the present invention, there is provided an endless belt stretched over a plurality of support rotating bodies, a recording material conveying member for carrying and conveying a recording material on the surface, and the recording material conveying member. Image forming means for forming an image on a recording material to be conveyed, a driving source for generating a rotational driving force, and a plurality of supporting rotating bodies on which the recording material conveying member is stretched by controlling the driving source. A belt according to claim 1, 2, 3, or 4 as the drive control means in an image forming apparatus having a drive control means for controlling the rotation of the drive support rotating body to which the rotational drive force from the drive source is transmitted. A drive control device is used.
According to a sixth aspect of the present invention, an image carrier comprising an endless belt stretched over a plurality of support rotators, an image forming means for forming an image on the image carrier, and a rotational driving force are generated. And the rotation of the driving support rotating body to which the rotational driving force from the driving source is transmitted among the plurality of supporting rotating bodies around which the image carrier is stretched. In the image forming apparatus that includes a drive control unit, and finally transfers an image on the image carrier onto the recording material to form an image on the recording material, the drive control unit includes: 2, 3, or 4 belt drive control devices are used.
In the image forming apparatus according to claim 5, the image forming unit forms images of different colors on a plurality of latent image carriers, and the images of the respective colors are An image is formed on the image carrier or on the recording material conveyed by the recording material conveying member so as to overlap each other.

In the present invention, target value data for canceling fluctuations in the belt moving speed due to periodic thickness fluctuations (belt thickness fluctuations) in the circumferential direction of the endless belt is stored in advance in the target value storage means. Then, based on the stored target value data, the rotation of the driving support rotating body is controlled so as to cancel the fluctuation of the belt moving speed due to the fluctuation of the belt thickness. Specifically, when the thick belt portion is in contact with the drive support rotator, the rotational angular velocity of the drive support rotator is lowered, and conversely, when the thin belt portion is in contact with the drive support rotator, the drive support rotator is rotated. Control to increase the angular velocity. The target value data can be obtained by grasping the belt thickness variation, and any method may be used for grasping the belt thickness variation.
In the present invention, the change in the thickness of the belt after being left standing, which changes when the belt is left, is grasped as follows. That is, as described above, as a result of the study by the present inventors, if the belt is left in a state where tension is applied after the belt driving is stopped, the belt thickness depends on the leaving time at a specific point on the belt moving path. Changed. The amount of change in the belt thickness according to the specific point and the standing time does not depend on the average thickness of the belt or variations in the belt thickness, based on the results of the study by the present inventors. The conclusion that it was decided unambiguously as long as the device configuration was decided. Therefore, if the apparatus configuration is determined, it is possible to grasp in advance the specific point at which the belt thickness changes due to leaving and the amount of change in the belt thickness according to the standing time. Therefore, the belt portion located at the specific point can be specified based on the belt stop position when the belt is stopped, and the thickness of the belt portion after being left for the left time is determined from the left time measured by the time measuring means. I can grasp it. Thereby, it is possible to grasp the belt thickness fluctuation after being left. In this way, since the belt stop position at the time of belt drive stop and the leaving time from the drive stop to the next drive start can be grasped, the change in belt thickness after the leave can be grasped. Then, it is possible to correct the target value data for canceling the fluctuation of the belt moving speed due to the fluctuation of the belt thickness after being left.
As described above, according to the present invention, appropriate target value data after being left can be obtained based on the stop position of the belt when the belt driving is stopped and the leaving time from the stop of driving to the start of the next driving. Thus, if the belt thickness fluctuation at the initial stage is grasped in advance and target value data corresponding to this is prepared, the stop position detecting means, the time measuring means, and the target value correcting means are referred to in Patent Document 1 described above. Target value data for canceling fluctuations in the belt moving speed due to fluctuations in the belt thickness after being left can be obtained by means that are cheaper than expensive filters used in the proposed belt drive control method.

  According to the present invention, even when the belt thickness at a specific point on the belt moving path changes due to being left, an excellent effect that the left belt can be driven at a constant moving speed at a low cost is exhibited. .

Embodiment 1
Hereinafter, an embodiment in which the present invention is applied to an electrophotographic direct color transfer color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus (hereinafter referred to as “embodiment 1”). Will be explained.
FIG. 2 is a schematic configuration diagram of the laser printer according to the present embodiment.
This laser printer has toner image forming portions 1Y, 1M, and 1C as four sets of image forming means for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). , 1K are arranged in order from the upstream side in the moving direction of the transfer paper 100 as the recording material. In the following description, the subscripts Y, M, C, and K of the symbols indicate members for yellow, magenta, cyan, and black, respectively. The toner image forming units 1Y, 1M, 1C, and 1K include photosensitive drums 11Y, 11M, 11C, and 11K, which are latent image carriers, and a developing unit, respectively. The arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel to each other and arranged at a predetermined pitch in the transfer paper moving direction. ing. In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer carries the optical writing unit 2, the paper feed cassettes 3 and 4, the registration roller pair 5, and the transfer paper 100, and each toner image forming unit. A transfer unit 6 as a belt driving device having a paper transport belt 60 as a recording material transport member that transports the recording material so as to pass through the transfer position, a fixing unit 7 of a belt fixing system, a paper discharge tray 8 and the like. In addition, a manual feed tray MF and a toner supply container TC are provided, and a waste toner bottle, a double-side reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line. The optical writing unit 2 includes a light source, a polygon mirror, an fθ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning with laser light based on image data.

FIG. 3 is an enlarged view showing a schematic configuration of the transfer unit 6.
The paper transport belt 60 used in the transfer unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ [Ωcm], and the material thereof is PVDF (polyvinylidene fluoride). The paper transport belt 60 is wound around support rollers 61 to 68 that are support rotating bodies so as to pass through the transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units. ing. Among these support rollers, the entrance roller 61 on the upstream side in the transfer paper moving direction is disposed on the outer peripheral surface of the paper conveyance belt 60 so that the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 80a is opposed. Yes. The transfer paper 100 that has passed between the two rollers 61 and 80 is electrostatically attracted onto the paper transport belt 60. The roller 63 is a drive roller that frictionally drives the paper transport belt 60, and is connected to a drive source (not shown) and rotationally driven in the direction of the arrow in the figure. A rotary encoder (not shown) is attached to the drive roller 63. A member denoted by reference numeral 81 is a mark detection sensor for reading an origin mark (not shown) written on the paper transport belt 60, and is fixed to the printer body.

  As a transfer electric field forming means for forming a transfer electric field at each transfer position, a transfer bias applying member 67Y is provided at a position facing each of the photosensitive drums 11Y, 11M, 11C, and 11K so as to be in contact with the back surface of the paper transport belt 60. , 67M, 67C, 67K. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller mandrel from each transfer bias power source 9Y, 9M, 9C, 9K. By the action of the applied transfer bias, a transfer charge is applied to the paper transport belt 60, and a transfer electric field having a predetermined strength is formed between the paper transport belt 60 and the surface of the photosensitive drum at each transfer position. Further, backup rollers 68 are provided in order to keep the contact between the transfer paper 100 and each of the photosensitive drums 11Y, 11M, 11C, and 11K in the transfer area and to obtain the best transfer nip. . The non-black transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around the rotation shaft 94. It is. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow. The entrance roller 61 and the suction roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state of FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoreceptors 11Y, 11M, 11C, and the entrance roller 61 is electrostatically charged. The suction roller 80 also moves downward. When a black-only image is formed, it is possible to avoid contact between the unused photosensitive drums 11Y, 11M, and 11C and the paper transport belt 60. Further, the black transfer bias applying member 67K and the backup roller 68 adjacent thereto are rotatably supported by the outlet bracket 98, and are rotatable about an axis 99 coaxial with the outlet roller 62. When the transfer unit 6 is attached to or detached from the printer body, the transfer unit 6K is rotated clockwise by operating a handle (not shown) to separate the transfer bias applying member 67K from the adjacent backup roller 68 from the black photosensitive drum 11K. I am trying to make it.

  A cleaning device 85 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the paper conveying belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the paper transport belt 60. A roller 64 is provided downstream of the driving roller 63 in the moving direction of the paper conveying belt 60 in a direction to push the outer peripheral surface of the paper conveying belt, and a winding angle around the driving roller 63 is secured. In the loop of the paper conveyance belt 60 further downstream from the roller 64, a tension roller 65 that applies tension to the paper conveyance belt 60 by a spring 69 as an urging means is provided.

  A one-dot chain line in FIG. 2 indicates a conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 sent out by the registration roller pair 5 at a predetermined timing is carried on the paper transport belt 60, transported toward the toner image forming portions 1Y, 1M, 1C, and 1K, and passes through the transfer nips. . The respective toner images developed on the photosensitive drums 11Y, 11M, 11C, and 11K of the respective toner image forming units are superimposed on the transfer paper 100 at the respective transfer nips, and are transferred by the effects of the transfer electric field and the nip pressure. Transferred onto the paper 100. By this superposition transfer, a full-color toner image is formed on the transfer paper 100. The surfaces of the photoconductive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.

  On the other hand, after the full color toner image is fixed by the fixing unit 7, the transfer paper 100 on which the full color toner image is formed corresponds to the first discharge direction B or the second discharge direction corresponding to the rotation posture of the switching guide. Heading in the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (such as a sorter or a binding device) (not shown), or again through a switchback unit for double-sided printing. Or transport to pair 5.

Next, a drive control system using an encoder will be described.
FIG. 4 is a block diagram showing the configuration of a control system that digitally controls the angular displacement of the pulse motor 110 based on the state detection signal of the drive roller 63 (here, the output signal of the encoder 111).
In FIG. 4, reference numeral 101 denotes a microcomputer including a microprocessor 102, a read only memory (ROM) 103, and a random access memory (RAM) 104. The microprocessor 102, the ROM 103, and the RAM 104 are connected via a bus 105, respectively. ing. Reference numeral 106 denotes a command generation device that outputs a state command signal for commanding a target angular displacement of the driven roller 66. The command generation device 106 generates an angular displacement command signal. The output side of the command generator 106 is also connected to the bus 105. Reference numeral 107 denotes a detection interface device that processes output pulses of the encoder 111 and converts them into digital numerical values. The detection interface device 107 includes a counter that counts the output pulses of the encoder 111, and the angular value of the driving roller 63 is obtained by multiplying the value counted by the counter by a conversion constant of a predetermined number of pulses and diagonal displacement. Convert to displacement. Reference numeral 108 denotes an interface for driving the pulse motor. The pulse motor driving interface 108 uses the calculation result (control output) of the microcomputer 101 as a pulse signal (for example, operating a power semiconductor constituting the pulse motor drive device 109). Control signal). The pulse motor drive device 109 operates based on the pulse signal from the pulse motor drive interface 108 and rotationally drives the pulse motor. As a result, the driving roller 63 is subjected to additional value control to a predetermined angular displacement by the command generator 106.

  The angular displacement of the drive roller 63 is detected by the encoder 111 and the detection interface device 107, is taken into the microcomputer 101, and the above operation is repeated. The origin signal of the paper conveyance belt 60, that is, the output signal of the mark detection sensor 81 is taken into the microcomputer 101 via the bus 105, and the target signal from the command generator 106 and the belt position are synchronized. . Here, in FIG. 4, a line connecting the pulse motor 110 and the transfer unit 6 corresponds to a power transmission system such as a driving gear.

FIG. 5 is a drive control block diagram for controlling the rotational angular displacement of the drive roller 63 by the pulse motor 110.
The output of the detection interface device 107 that processes the output of the encoder 111, that is, the angular displacement information P (i−1) of the drive roller 63 is given to the calculation unit 121. The calculation unit 121 calculates a difference e (i) between the target angular displacement Ref (i) of the driving roller 63 and the angular displacement P (i−1) of the driving roller 63, which is a control target value. This e (i) is input to the control controller unit 122. The control controller unit 122 is configured by a PI control system, for example. The e (i) calculated by the calculation unit 121 is integrated in the block 123, multiplied by a constant KI in the block 124, and given to the calculation unit 125. At the same time, e (i) calculated by the calculation unit 121 is multiplied by a constant KP in a block 126 and is given to the calculation unit 125. The calculation unit 125 adds two input signals from the blocks 124 and 126 and gives the result to the calculation unit 127. Thereafter, the calculation unit 127 adds a constant pulse input Refp_c to determine the drive pulse frequency u (i). The low-pass filter is set between the control controller unit 122 and the motor driver. That is, u (i) is in a state where a low-pass filter is applied. The drive pulse frequency u (i) obtained by the calculation unit 127 is output to the pulse motor 110 via the pulse motor drive interface 108 and the pulse motor drive device 109, and the drive roller 63 rotates through the transmission system. The above loop operation is repeated.
Here, the control controller unit 122 uses a PI control system as an example, but is not limited thereto.

  All the above operations are performed by numerical operations in the microcomputer 101 and can be easily realized. Further, Refp_c is the number of pulses uniquely determined based on the angular velocity of the driving roller 63 and the reduction ratio of the reduction system. In the first embodiment, the range in which the step-out phenomenon does not occur during motor driving. It is also possible to select arbitrarily. Further, Ref (i) can be easily obtained by adding a fluctuation component caused by belt thickness fluctuation obtained by a method described later to a value obtained by integrating the target constant angular velocity of the driving roller 63.

Next, a method for obtaining the fluctuation component due to the belt thickness fluctuation will be described.
In the first embodiment, as described above, the angular displacement of the driving roller 63 is controlled to the target angular displacement Ref (i). Therefore, in the first embodiment, as the fluctuation component due to the belt thickness fluctuation, the deviation (belt position fluctuation) with respect to the target position of the paper transport belt 60 is converted into the angular displacement of the driving roller 63. However, for the sake of simplification of description, in the following description, a belt moving speed that varies due to a belt thickness fluctuation is obtained, and this is integrated to obtain a belt position fluctuation.

  When obtaining the belt moving speed that fluctuates due to the belt thickness fluctuation, first, an encoder is attached to the driven roller 66, the pulse motor 110 is rotated at a constant angular velocity, and based on the encoder output of the driven roller 66 at that time, The encoder output fluctuation component (amplitude) and the phase from the belt reference position are measured. In the first embodiment, since the belt position is detected based on the result of detecting the belt origin mark by the mark detection sensor 81, the phase difference from the belt reference position can be easily obtained. Next, a target value for canceling the fluctuation of the belt moving speed due to the belt thickness fluctuation is obtained by multiplying the amplitude of the obtained fluctuation component by a predetermined coefficient and adding the predetermined coefficient to the obtained phase. Data, that is, the target angular displacement Ref (i). These coefficients are values uniquely determined mainly by the belt passing configuration.

ただし、「Ｒ_d」は駆動ローラ６３のローラ実効半径であり、「Ｒ_e」は従動ローラ６６のローラ実効半径である。また、「θ_d」は駆動ローラ６３に対する紙搬送ベルト６０の巻付角であり、「θ_e」は従動ローラ６６に対する紙搬送ベルト６０の巻付角である。また、「κ_d」は、駆動ローラ６３のベルト巻付角θ_d、ベルト材質、ベルト層構造等によって決まる駆動ローラ６３のベルト厚み実効係数であり、ベルト厚みがベルト移動速度Ｖに影響する度合いを決定するパラメータである。同様に、「κ_e」は、従動ローラ６６のベルト厚み実効係数である。これらのベルト厚み実効係数κ_d、κ_eは、一般に、ベルト材質が均一で一層構造のベルトを用い、かつ、ベルト巻付角θ_d、θ_eが十分に大きいとき、いずれも０．５となる。また、「Ｂ_t0」は紙搬送ベルト６０の平均厚みである。また、「α」は、紙搬送ベルト６０の初期位相である。また、「Ｄ_d」は、下記の数３で示すものである。また、「τ」は、駆動ローラ６３から従動ローラ６６まで紙搬送ベルト６０が移動するのに要する平均時間（遅れ時間）である。

More specifically, the belt position error (deviation amount) A generated in the belt surface movement direction due to the belt thickness variation of the belt portion wound around the drive roller 63 can be expressed by the following equation (1). Further, the belt position error B generated in the belt surface movement direction due to the belt thickness variation of the belt portion wound around the driven roller 66 can be expressed by the following equation (2).

However, “R _d ” is the effective roller radius of the driving roller 63, and “R _e ” is the effective roller radius of the driven roller 66. “Θ _d ” is the winding angle of the paper conveyance belt 60 around the driving roller 63, and “θ _e ” is the winding angle of the paper conveyance belt 60 around the driven roller 66. “Κ _d ” is the belt thickness effective coefficient of the driving roller 63 determined by the belt winding angle θ _d of the driving roller 63, the belt material, the belt layer structure, and the like, and the degree to which the belt thickness affects the belt moving speed V. Is a parameter for determining Similarly, “κ _e ” is a belt thickness effective coefficient of the driven roller 66. These belt thickness effective coefficients κ _d and κ _e are generally 0.5 when the belt material is uniform and a single layer belt is used and the belt winding angles θ _d and θ _e are sufficiently large. Become. “B _t0 ” is the average thickness of the paper transport belt 60. “Α” is the initial phase of the paper transport belt 60. “D _d ” is represented by the following formula 3. “Τ” is an average time (delay time) required for the paper transport belt 60 to move from the driving roller 63 to the driven roller 66.

The belt position error C for one belt period in the belt portion wound around the driven roller 66 is a composite wave of A and B, and is expressed by the following equation (4). However, the symbol K in the equation 4 is represented by the following equation 5, and the symbol β in the equation 4 is represented by the following equation 6.

Since the detection result based on the encoder output of the driven roller 66 when the paper transport belt 60 is moving at a constant speed is B as described above, the belt is controlled at a constant speed by controlling the C to be equal to B. It will be possible. Comparing B and C, it can be seen that the value shown in the following equation 7 should be applied to the amplitude, and that -β + τ should be added to the phase. Thus, a target value can be created. Here, the target position fluctuation can be calculated by integrating the obtained target speed.

Next, a change in the thickness of the belt portion in the vicinity of the entrance roller 61 (a specific point) when the paper conveyance belt 60 in the laser printer of the first embodiment is left in the drive stopped state will be described.
FIG. 6 is a graph showing a change in the thickness of the belt portion in the vicinity (specific point) of the entrance roller 61 according to the standing time. In this graph, the amount of belt thickness change in the vicinity of the entrance roller 61 is plotted on the vertical axis, and the standing time is plotted on the horizontal axis.
Until now, it was thought that the belt thickness did not change due to neglecting. However, as shown in the graph of FIG. 6, according to the experiments of the present inventors, the belt thickness at a specific point may vary according to the neglecting time. confirmed. And, according to the study by the present inventors, the amount of belt thickness change according to the specific point where the belt thickness changes due to neglect and the neglect time at the specific point does not depend on the average thickness of the belt or the belt thickness variation, It was concluded that if the device configuration such as the material of the belt and the belt passing configuration is determined, it is uniquely determined. Therefore, for example, in the case of the apparatus configuration according to the first embodiment, the belt thickness changes in the vicinity of the entrance roller 61 when the belt is left, regardless of the belt thickness variation, and the length of the belt depends on the leaving time. The amount of change is also as shown in the graph of FIG.

[Target value data correction example 1]
Next, a correction example of target angular displacement Ref (i) that is target value data (hereinafter, this correction example is referred to as “correction example 1”) will be described.
FIG. 1 is a flowchart showing a flow of control in the first correction example.
When a drive stop command is received after driving the paper transport belt 60 (S1), first, the drive of the pulse motor 110 is stopped (S2), and the pulse motor is used to grasp the stop position of the paper transport belt 60. The stop position (angular displacement) of 110 is stored (S3). Further, the time t1 when the drive is stopped is also stored (S4). These stop position data and time t1 data may be stored in a nonvolatile memory. Thereafter, when the drive signal of the paper conveying belt 60 is turned on (S5), the time t2 at that time is stored (S6), and the leaving time is obtained from the difference between the time t1 and the time t2 (S7). Then, from the data of the graph shown in FIG. 6 based on the standing time and the stop position stored in S2, the target angular displacement Ref (i) is changed after the belt thickness changes at the specific point by leaving the standing time. A correction value for obtaining a target angular displacement corresponding to the belt thickness fluctuation is obtained (S8). Thereafter, the pulse motor 110 is driven using the obtained corrected target angular displacement Ref (i) (S9).

  By correcting the target angular displacement Ref (i) in this way, even if the thickness of the belt portion in the vicinity of the entrance roller 61 is changed by leaving the paper conveying belt 60 in a driving stopped state, The paper transport belt 60 can be driven at a constant speed.

[Target value data correction example 2]
Next, another correction example of the target angular displacement Ref (i) that is target value data (hereinafter, this correction example is referred to as “correction example 2”) will be described.
FIG. 7 is a flowchart showing the flow of control in the second correction example.
When the drive stop command is received after starting the paper transport belt 60 (S1), in the second correction example, the pulse motor 110 is driven so that the paper transport belt 60 stops at a predetermined reference stop position. Is stopped (S10). As a result, the stop position of the paper transport belt 60 is fixed, so that it is not necessary to grasp the stop position of the belt every time the belt drive is stopped as in the first correction example. Subsequent control is the same as in the case of the correction example 1, and the description is omitted.

Here, in the second correction example, if the reference stop position is set so that the thickest belt portion in the belt circumferential direction before being left is stopped at the specific point, the phase of the belt thickness fluctuation changes before and after being left. There is no. Therefore, it is not necessary to correct the phase of the target angular displacement Ref (i) in S8, and the correction value can be easily calculated.
In the second correction example, if the reference stop position is set such that the thinnest belt portion in the belt circumferential direction before being left is stopped at the specific point, the amplitude of the belt thickness fluctuation can be reduced. Therefore, the change width for changing the rotation angular velocity of the pulse motor 110 according to the belt thickness variation can be reduced, and more accurate drive control can be performed.

[Embodiment 2]
Next, another embodiment (hereinafter, this embodiment is referred to as “embodiment 2”) in which the present invention is applied to an electrophotographic intermediate transfer color copier as an image forming apparatus will be described.
FIG. 8 is a schematic configuration diagram showing a color copying machine according to the second embodiment.
The copying machine main body 210 includes a photosensitive drum 212 which is a latent image carrier, slightly to the right in the figure from the center in the outer case 211. Around the photosensitive drum 212, a charger 213 installed on the photosensitive drum 212 is sequentially rotated in the direction indicated by the arrow (counterclockwise direction), and a rotary developing device 214, an intermediate transfer unit 215, and a cleaning unit. A device 216, a static eliminator 217, and the like are arranged. On these charger 213, rotary developing device 214, cleaning device 216, and static eliminator 217, an optical writing device as an exposure unit, for example, a laser writing device 218 is installed. The rotary developing device 214 includes developing devices 220A, 220B, 220C, and 220D having developing rollers 221 that store toners of yellow, magenta, cyan, and black, respectively, and rotate around a central axis to rotate each color. The developing devices 220A, 220B, 220C, and 220D are selectively moved to a developing position that faces the outer periphery of the photosensitive drum 212.

In the intermediate transfer unit 215, an intermediate transfer belt 224 as an intermediate transfer member including an endless belt as an image carrier is wound around a plurality of rollers 223, and the intermediate transfer belt 224 comes into contact with the photosensitive drum 212. . A primary transfer device 25 is installed inside the intermediate transfer belt 224, and a secondary transfer device 226 and a cleaning device 227 are installed outside the intermediate transfer belt 224. The cleaning device 227 is provided so as to be able to contact with and separate from the intermediate transfer belt 224.
The laser writing device 218 receives an image signal of each color from the image reading device 229 via an image processing unit (not shown), and the laser beam L that is sequentially modulated by the image signal of each color is uniformly charged in the photosensitive drum 212. To expose the photosensitive drum 212 to form an electrostatic latent image on the photosensitive drum 212.
The image reading device 229 color-separates and reads the image of the document G set on the document table 230 provided on the upper surface of the copier body 210, and converts it into an electrical image signal. The recording medium conveyance path 232 conveys a recording medium such as a sheet from right to left. A registration roller pair 233 is installed in the recording medium conveyance path 232 in front of the intermediate transfer unit 215 and the transfer device 226, and the conveyance belt 234, the fixing device 235, and the paper discharge roller are located downstream of the intermediate transfer unit 215 and the transfer device 226. A pair 236 is arranged.

The copying machine main body 210 is placed on a paper feeding device 250. A plurality of paper feed cassettes 251 are provided in multiple stages in the paper feed device 250, and any one of the paper feed rollers 252 is selectively driven to send a recording medium from any one of the paper feed cassettes 251. . This recording medium is conveyed to the recording medium conveyance path 232 through the automatic paper feeding path 237 in the copying machine main body 210.
A manual feed tray 238 is provided on the right side of the copying machine main body 210 so as to be openable and closable. A recording medium inserted from the manual feeding tray 238 is conveyed to the recording medium conveyance path 232 through the manual paper feed path 239 in the copying machine main body 210. The A paper discharge tray (not shown) is detachably attached to the left side of the copying machine main body 210, and the recording medium discharged by the paper discharge roller pair 236 through the recording medium conveyance path 232 is accommodated in the paper discharge tray.

In this color copying machine, when making a color copy, when a document G is set on the document table 230 and a start switch (not shown) is pressed, a copying operation is started. First, the image reading device 229 color-separates and reads the image of the document G on the document table 230.
At the same time, the recording medium is selectively sent out from the paper feeding cassette 251 in the paper feeding device 250 by the paper feeding roller 252, and this recording medium hits the registration roller pair 233 through the automatic paper feeding path 237 and the recording medium conveyance path 232. Stop.
The photosensitive drum 212 rotates in the counterclockwise direction, and the intermediate transfer belt 224 rotates in the clockwise direction by the rotation of the driving roller among the plurality of rollers 223. The photosensitive drum 212 is uniformly charged by the charger 213 as it rotates, and the laser beam modulated by the first color image signal applied from the image reading device 229 to the laser writing device 218 via the image processing unit. Irradiation from the laser writing device 218 forms an electrostatic latent image.

The electrostatic latent image on the photosensitive drum 212 is developed by the first color developing device 220A of the rotary developing device 214 to become a first color image, and the first color image on the photosensitive drum 212 is intermediately transferred by the transfer device 225. Transferred to the belt 224. The photosensitive drum 212 is cleaned by the cleaning device 216 after the transfer of the image of the first color to remove the residual toner, and is neutralized by the static eliminator 217.
Subsequently, the photosensitive drum 212 is uniformly charged by the charger 213, and laser light modulated by the image signal of the second color applied from the image reading device 229 to the laser writing device 218 via the image processing unit is laser-induced. Irradiation from the writing device 218 forms an electrostatic latent image. The electrostatic latent image on the photoconductive drum 212 is developed by the second color developing device 220B of the rotary developing device 214 into a second color image, and the second color image on the photoconductive drum 212 is intermediate transferred by the transfer device 225. The image is transferred onto the belt 224 so as to overlap the first color image. The photosensitive drum 212 is cleaned by the cleaning device 216 after the transfer of the second color image, the residual toner is removed, and the static eliminator 217 is discharged.

Next, the photosensitive drum 212 is uniformly charged by the charger 213, and the laser beam modulated by the image signal of the third color applied from the image reading device 229 to the laser writing device 218 via the image processing unit is a laser beam. Irradiation from the writing device 218 forms an electrostatic latent image. The electrostatic latent image on the photoconductive drum 212 is developed by the third color developing device 220C of the rotary developing device 214 to become a third color image, and the third color image on the photoconductive drum 212 is intermediated by the transfer device 225. The first color image and the second color image are superimposed on the transfer belt 224 and transferred. The photosensitive drum 212 is cleaned by the cleaning device 216 after the transfer of the image of the third color, the residual toner is removed, and the static eliminator 217 is discharged.
Further, the photosensitive drum 212 is uniformly charged by the charger 213, and laser light modulated by the image signal of the fourth color applied from the image reading device 229 to the laser writing device 218 via the image processing unit is laser-written. Irradiation from the device 218 forms an electrostatic latent image. The electrostatic latent image on the photosensitive drum 212 is developed by the fourth color developing device 220D of the rotary developing device 214 to become a fourth color image, and the fourth color image on the photosensitive drum 212 is intermediately transferred by the transfer device 225. A full-color image is formed on the belt 224 by overlapping and transferring the first-color image, the second-color image, and the third-color image.
The photosensitive drum 212 is cleaned by the cleaning device 216 after the transfer of the image of the fourth color, the residual toner is removed, and the static eliminator 217 is discharged.

Then, the registration roller pair 233 is rotated at a timing to send out a recording medium, and a full-color image on the intermediate transfer belt 224 is transferred to the recording medium by the transfer device 226. This recording medium is transported by a transport belt 234, a full color image is fixed by a fixing device 235, and discharged to a discharge tray by a discharge roller pair 236. Further, the intermediate transfer belt 224 is cleaned by a cleaning device 227 after the transfer of the full-color image to remove residual toner.
The operation for forming a four-color superimposed image has been described above. When a three-color superimposed image is formed, three different single-color images are sequentially formed on the photosensitive drum 212 and transferred onto the intermediate transfer belt 224. And then transferred to a recording medium at once. In the case of forming a two-color superimposed image, two different single-color images are sequentially formed on the photosensitive drum 212, transferred onto the intermediate transfer belt 224, and then transferred to a recording medium at a time.

In such a color copying machine, the driving accuracy of the intermediate transfer belt 224, which is an image carrier, greatly affects the quality of the final image, and it is desired to drive these with higher accuracy.
Therefore, in the second embodiment, the intermediate transfer belt 224 is feedback-controlled using the same drive device as the paper conveyance belt in the first embodiment described above. Therefore, even if the belt thickness at a specific point is changed by leaving the intermediate transfer belt 224 in the drive stop state, the intermediate transfer belt 224 can be driven at a constant speed after the belt is left. As a result, even if the belt thickness at a specific point of the intermediate transfer belt 224 changes due to leaving, it is possible to obtain a high-quality image without color misregistration with respect to the image when left.

[Embodiment 3]
Next, still another embodiment (hereinafter, this embodiment is referred to as “embodiment 3”) in which the present invention is applied to an electrophotographic intermediate transfer color copier as an image forming apparatus will be described.
FIG. 9 is a schematic configuration diagram of the color copying machine according to the third embodiment.
In FIG. 9, a photosensitive belt 301 as an image carrier is an endless photosensitive member in which a photosensitive layer such as an organic optical semiconductor (OPC) is formed in a thin film on an outer peripheral surface of a closed loop NL belt base material. It is a body belt. The photoreceptor belt 301 is supported by photoreceptor transport rollers 302 to 304 as three support rotating bodies, and is rotated in the direction of arrow A by a drive motor (not shown).

  Around the photosensitive belt 301, a charger 305, an exposure optical system (hereinafter referred to as LSU) 306 as exposure means, and a developer unit for each color of black, yellow, magenta, and cyan, in the photosensitive drum rotation direction indicated by an arrow A. 307 to 310, an intermediate transfer unit 311, a photosensitive member cleaning unit 312, and a static eliminator 313 are provided. The charger 305 is applied with a high voltage of about −4 to 5 kV from a power supply device (not shown), and charges the portion of the photosensitive belt 301 facing the charger 305 to give a uniform charging potential.

  The LSU 306 sequentially modulates the light intensity and pulse width of each color image signal from a gradation converting means (not shown) by a laser drive circuit (not shown), and a semiconductor laser (not shown) with the modulated signal. ) Is obtained, and the photosensitive belt 301 is scanned by the exposure light beam 314 to sequentially form electrostatic latent images corresponding to the image signals of the respective colors on the photosensitive belt 301. The seam sensor 315 detects the seam of the photosensitive belt 301 formed in a loop shape. When the seam sensor 315 detects the seam of the photosensitive belt 301, the seam of the photosensitive belt 301 is avoided. The timing controller 316 controls the light emission timing of the LSU 306 so that the electrostatic latent image formation angular displacements of the respective colors become the same.

  Each of the developing units 307 to 310 stores toner corresponding to each developing color, and is selectively photosensitive belt at a timing corresponding to an electrostatic latent image corresponding to an image signal of each color on the photosensitive belt 301. The full-color image is formed by overlapping four colors by contacting the toner 301 and developing the electrostatic latent image on the photosensitive belt 301 with toner to form each color image.

  The intermediate transfer unit 311 includes a drum-shaped intermediate transfer body (transfer drum) 317 in which a belt-shaped sheet made of a conductive resin or the like is wound around a metal tube such as aluminum, and an intermediate formed by forming rubber or the like into a blade shape. The intermediate transfer member cleaning unit 318 is separated from the intermediate transfer member 317 while the four-color superimposed image is formed on the intermediate transfer member 317. The intermediate transfer member cleaning unit 318 contacts the intermediate transfer member 317 only when the intermediate transfer member 317 is cleaned, and removes toner remaining without being transferred from the intermediate transfer member 317 to the recording paper 319 as a recording medium. The recording paper is sent one by one from the recording paper cassette 320 to the paper transport path 322 by the paper feed roller 321.

  A transfer unit 323 serving as a transfer unit transfers a full-color image on the intermediate transfer member 317 to a recording sheet 319. The transfer belt 324 is formed of a conductive rubber or the like in a belt shape, and the intermediate transfer member 317 A transfer unit 325 for applying a transfer bias for transferring the full color image to the recording paper 319 to the intermediate transfer member 317, and the recording paper 319 electrostatically transferred to the intermediate transfer member 317 after the full color image is transferred to the recording paper 319. The separator 326 applies a bias to the intermediate transfer member 317 so as to prevent sticking.

  The fixing device 327 includes a heat roller 328 having a heat source therein and a pressure roller 329. The full color image transferred on the recording paper 319 is rotated between recording rollers of the heat roller 328 and the pressure roller 329. Accordingly, pressure and heat are applied to the recording paper 319 to fix the full color image on the recording paper 319 to form a full color image.

The color copy having the above configuration operates as follows. Here, the description will proceed assuming that the development of the electrostatic latent image is performed in the order of black, cyan, magenta, and yellow.
The photosensitive belt 301 and the intermediate transfer member 317 are driven in the directions of arrows A and B by respective drive sources (not shown). In this state, first, a high voltage of about −4 to 5 kV is applied to the charger 305 from a power supply device (not shown), and the charger 305 uniformly charges the surface of the photosensitive belt 301 to about −700 V. . Next, the exposure belt 314 of the laser beam corresponding to the black image signal is irradiated from the LSU 306 to the photosensitive belt 301, and the charge on the portion irradiated with the exposure beam 314 disappears from the photosensitive belt 301 and an electrostatic latent image is formed. It is formed.

  On the other hand, the black developing device 307 is brought into contact with the photosensitive belt 301 at a predetermined timing. The black toner in the black developing device 307 is given a negative charge in advance, and the black toner adheres only to the portion (electrostatic latent image portion) where the charge is eliminated by the irradiation of the exposure light beam 314 on the photosensitive belt 301. The so-called negative-positive process is performed. The black toner image formed on the surface of the photosensitive belt 301 by the black developing device 307 is transferred to the intermediate transfer member 317. Residual toner that has not been transferred from the photoreceptor belt 301 to the intermediate transfer body 317 is removed by the photoreceptor cleaning means 312, and the charge on the photoreceptor belt 301 is removed by the charge eliminator 313.

  Next, the charger 305 uniformly charges the surface of the photoreceptor belt 301 to about −700V. Then, the exposure belt 314 of the laser beam corresponding to the cyan image signal is emitted from the LSU 306 to the photosensitive belt 301, and the charge on the portion irradiated with the exposure radiation 314 disappears from the photosensitive belt 301 to form an electrostatic latent image. Is done.

  On the other hand, a cyan developing device 308 is brought into contact with the photosensitive belt 301 at a predetermined timing. The cyan toner in the cyan developing unit 308 is given a negative charge in advance, and the cyan toner adheres only to the portion (electrostatic latent image portion) where the charge has disappeared by the exposure light beam 314 irradiation on the photosensitive belt 301. The so-called negative-positive process is performed. The cyan toner image formed on the surface of the photoreceptor belt 301 by the cyan developing device 308 is transferred onto the intermediate transfer member 317 so as to overlap the black toner image. Residual toner that has not been transferred from the photoreceptor belt 301 to the intermediate transfer body 317 is removed by the photoreceptor cleaning means 312, and the charge on the photoreceptor belt 301 is removed by the charge eliminator 313.

  Next, the charger 305 uniformly charges the surface of the photoreceptor belt 301 to about −700V. Then, the exposure belt 314 of the laser beam corresponding to the magenta image signal is irradiated from the LSU 306 to the photosensitive belt 301, and the photosensitive belt 301 loses the charge of the portion irradiated with the exposure beam 314, thereby forming an electrostatic latent image. Is done.

  On the other hand, a magenta developer 309 is brought into contact with the photosensitive belt 301 at a predetermined timing. The magenta toner in the magenta developing unit 309 is negatively charged in advance, and the magenta toner adheres only to the portion (electrostatic latent image portion) where the charge has disappeared due to the exposure light beam 314 irradiation on the photosensitive belt 301. The so-called negative-positive process is performed. The magenta toner image formed on the surface of the photoreceptor belt 301 by the magenta developing unit 309 is transferred onto the intermediate transfer member 317 so as to overlap the black toner image and the cyan toner image. Residual toner that has not been transferred from the photoreceptor belt 301 to the intermediate transfer body 317 is removed by the photoreceptor cleaning means 312, and the charge on the photoreceptor belt 301 is removed by the charge eliminator 313.

  Further, the charger 305 uniformly charges the surface of the photoreceptor belt 301 to about −700V. Then, the exposure belt 314 of the laser beam corresponding to the yellow image signal is irradiated from the LSU 306 to the photosensitive belt 301, and the photosensitive belt 301 loses the electric charge of the portion irradiated with the exposure beam 314 and forms an electrostatic latent image. Is done.

  On the other hand, the yellow developing device 310 is brought into contact with the photosensitive belt 301 at a predetermined timing. The yellow toner in the yellow developing unit 310 is given a negative charge in advance, and the yellow toner adheres only to the portion (electrostatic latent image portion) where the charge is eliminated by the irradiation of the exposure light beam 314 on the photosensitive belt 301. The so-called negative-positive process is performed. The yellow toner image formed on the surface of the photoreceptor belt 301 by the yellow developing device 310 is transferred onto the intermediate transfer member 317 so as to overlap the black toner image, the cyan toner image, and the magenta toner image, and a full color image is transferred onto the intermediate transfer member 317. Is formed. Residual toner that has not been transferred from the photoreceptor belt 301 to the intermediate transfer body 317 is removed by the photoreceptor cleaning means 312, and the charge on the photoreceptor belt 301 is removed by the charge eliminator 313.

  In the full-color image formed on the intermediate transfer member 317, the transfer unit 323 that has been separated from the intermediate transfer member 317 so far comes into contact with the intermediate transfer member 317, and a high voltage of about +1 kV is applied to the transfer unit 325 in the power supply device (FIG. (Not shown), the transfer device 325 collectively transfers the recording paper 319 transported along the paper transport path 322 from the recording paper cassette 320.

  Further, a voltage is applied from the power supply device to the separator 326 so that an electrostatic force that attracts the recording paper 319 acts, and the recording paper 319 is peeled off from the intermediate transfer member 317. Subsequently, the recording paper 319 is sent to the fixing device 327, where the full color image is fixed by the nipping pressure between the heat roller 328 and the pressure roller 329 and the heat of the heat roller 328, and the paper discharge tray 330 sets the paper discharge tray. It is discharged to 331.

  Further, residual toner on the intermediate transfer member 317 that has not been transferred onto the recording paper 319 by the transfer unit 323 is removed by the intermediate transfer member cleaning unit 318. The intermediate transfer member cleaning unit 318 is at an angular displacement away from the intermediate transfer member 317 until a full color image is obtained. After the full color image is transferred to the recording paper 319, the intermediate transfer member 317 comes into contact with the intermediate transfer member 317 and moves onto the intermediate transfer member 317. Residual toner is removed. The full color image formation for one sheet is completed by the series of operations described above.

In such a color copying machine, the rotational accuracy of the photosensitive belt 301 as an image carrier greatly affects the quality of the final image, and particularly high-precision driving of the photosensitive belt 301 with high accuracy is desired.
Therefore, in the third embodiment, the photosensitive belt 301 is feedback-controlled using the same driving device as the paper conveyance belt in the first embodiment described above. Therefore, even if the belt thickness at a specific point is changed by leaving the photosensitive belt 301 in the drive stop state, the photosensitive belt 301 can be driven at a constant speed after the standing. As a result, even if the belt thickness at a specific point of the photosensitive belt 301 changes due to leaving, a high-quality image without color misregistration can be obtained with respect to the image when left.

[Embodiment 4]
Next, still another embodiment (hereinafter, this embodiment is referred to as “embodiment 4”) in which the present invention is applied to an electrophotographic intermediate transfer type tandem color copier as an image forming apparatus. explain.
FIG. 10 is a schematic configuration diagram of a color copying machine according to the fourth embodiment.
In FIG. 10, reference numeral 491 is a copying machine main body, 492 is a paper feed table on which it is placed, 493 is a scanner mounted on the copying machine main body 491, and 494 is an automatic document feeder (ADF) further mounted thereon.
The copying machine main body 491 is provided with an intermediate transfer belt 410 as an image carrier, which is an endless belt, in the center. The intermediate transfer belt 410 corresponds to an endless belt in the claims. As shown in FIG. 10, in the illustrated example, it is wound around three support rollers 414, 415, 416 and can be rotated and conveyed clockwise in the figure.
In this illustrated example, an intermediate transfer belt cleaning device 417 that removes residual toner remaining on the intermediate transfer belt 410 after image transfer is provided to the left of the second support roller 415 among the three. Further, on the intermediate transfer belt 410 stretched between the first support roller 414 and the second support roller 415 of the three, four of black, cyan, magenta, and yellow are arranged along the transport direction. The tandem image forming apparatus 420 is configured by arranging two image forming units 418 side by side.

  An exposure device 421 is provided on the tandem image forming apparatus 420 as shown in FIG. On the other hand, a secondary transfer device 422 is provided on the opposite side of the intermediate transfer belt 410 from the tandem image forming device 420. In the illustrated example, the secondary transfer device 422 is configured such that a secondary transfer belt 424 serving as a recording material conveying member, which is an endless belt, is stretched between two rollers 423, and the second transfer device 422 is interposed via an intermediate transfer belt 410. 3 is pressed against the support roller 416 to transfer the image on the intermediate transfer belt 410 to the sheet.

Next to the secondary transfer device 422, a fixing device 425 for fixing the transferred image on the sheet is provided. The fixing device 425 is configured by pressing a pressure roller 427 against a fixing belt 426 that is an endless belt.
The secondary transfer device 422 is also provided with a sheet conveyance function for conveying the image-transferred sheet to the fixing device 425. Of course, a non-contact charger may be arranged as the secondary transfer device 422. In such a case, it is difficult to provide this sheet conveying function together.
In the illustrated example, under such a secondary transfer device 422 and a fixing device 425, a sheet reversing device 428 for reversing the sheet to record images on both sides of the sheet in parallel with the tandem image forming device 420 described above. Is provided.

When making a copy using the color copying machine having the above-described configuration, a document is set on the document table 430 of the automatic document feeder 494. Alternatively, the automatic document feeder 494 is opened, a document is set on the contact glass 432 of the scanner 493, and the automatic document feeder 494 is closed and pressed by it.
When a start switch (not shown) is pressed, when the document is set on the automatic document feeder 494, the document is transported and moved onto the contact glass 432, and then the document is set on the other contact glass 432. At that time, the scanner 493 is immediately driven to travel on the first traveling body 433 and the second traveling body 434. Then, the first traveling body 433 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 434 and reflects by the mirror of the second traveling body 434 and passes through the imaging lens 435. The document is placed in a reading sensor 436 and the original content is read.

  When a start switch (not shown) is pressed, one of the support rollers 414, 415, and 416 is driven to rotate by the drive motor (not shown), the other two support rollers are driven to rotate, and the intermediate transfer belt 410 is rotated and conveyed. To do. At the same time, the individual image forming means 418 rotates the photoreceptor 440 to form black, yellow, magenta, and cyan single color images on each photoreceptor 440. Then, along with the conveyance of the intermediate transfer belt 410, these single color images are sequentially transferred to form a composite color image on the intermediate transfer belt 410.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 442 of the paper feed table 492 is selectively rotated, and a sheet is fed out from one of the paper feed cassettes 444 provided in the paper bank 443 in multiple stages, and the separation roller 445 is fed. Are separated one by one into the paper feed path 446, transported by the transport roller 447, guided to the paper feed path 448 in the copying machine main body 491, and abutted against the registration roller 449 and stopped.
Alternatively, the sheet feed roller 450 is rotated to feed out the sheets on the manual feed tray 451, separated one by one by the separation roller 452, put into the manual feed path 453, and abutted against the registration roller 449 and stopped.
Then, the registration roller 449 is rotated in synchronization with the composite color image on the intermediate transfer belt 410, the sheet is fed between the intermediate transfer belt 410 and the secondary transfer device 422, and is transferred by the secondary transfer device 422. A color image is recorded on the sheet.

  The image-transferred sheet is conveyed by the secondary transfer device 422 and sent to the fixing device 425. The fixing device 425 applies heat and pressure to fix the transferred image, and is then switched by the switching claw 455 and discharged. The paper is discharged at 456 and stacked on the paper discharge tray 457. Alternatively, it is switched by the switching claw 455 and put into the sheet reversing device 428, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the paper discharge tray 457 by the discharge roller 456.

  On the other hand, the intermediate transfer belt 410 after image transfer is removed by the intermediate transfer belt cleaning device 417 to remove residual toner remaining on the intermediate transfer belt 410 after image transfer, and prepares for the image formation by the tandem image forming device 420 again.

Also in the color copying machine having the above configuration, the driving accuracy of the intermediate transfer belt 410 as an intermediate transfer member serving as an image carrier greatly affects the quality of the final image, and it is desired to drive these with higher accuracy.
Therefore, in the fourth embodiment, the intermediate transfer belt 410 is feedback-controlled using the same driving device as the paper conveyance belt in the first embodiment described above. Therefore, even if the belt thickness at a specific point is changed by leaving the intermediate transfer belt 410 in the drive stop state, the intermediate transfer belt 410 can be driven at a constant speed after the belt is left. As a result, even if the belt thickness at a specific point of the intermediate transfer belt 410 changes due to leaving, it is possible to obtain a high-quality image without color misregistration with respect to the image when left.

As described above, in the image forming apparatuses according to the first, second, third, and fourth embodiments described above, the circumferences of the endless belts 60, 224, 301, and 410 that are stretched around the support rollers 61 to 68 that are a plurality of support rotating bodies. RAM 104 as target value storage means for storing target angular displacement Ref (i), which is target value data for canceling fluctuations in belt movement speed due to periodic belt thickness fluctuations in the direction, and target angles stored in RAM 104 The drive control system shown in FIG. 4 as rotation control means for controlling the rotation of the drive roller 63 which is a drive support rotating body to which the rotational drive force is transmitted among the support rollers 61 to 68 based on the displacement Ref (i). And attached to a driving roller 63 as stop position detecting means for detecting the belt stop position when the belts 60, 224, 301 and 410 are stopped. Encoder 111 and microcomputer 101, and microcomputer 101 as time measuring means for measuring the standing time from the stop of driving of belts 60, 224, 301 and 410 to the start of the next driving. Is located at a specific point where the belt thickness changes when the belts 60, 224, 301, and 410 are left in the drive stop state based on the stop position detected (in the vicinity of the entrance roller 61 in the first embodiment). Based on the time measurement result of the microcomputer 101, the target angular displacement corresponding to the belt thickness variation after the belt thickness change of the belt portion is determined based on the time measurement result of the microcomputer 101. To the target angular displacement Ref (i) stored in the RAM 104. And a belt driving controller and a microcomputer 101 as the target value correcting means for. As a result, as described above, the belt is kept at a constant speed even after being left based on the stop positions of the belts 60, 224, 301, and 410 when the belt driving is stopped and the leaving time from the driving stop to the next driving start. An appropriate target angular displacement Ref (i) that can be driven by
Further, in the above-described correction example 1, the microcomputer 101 uses the RAM 104 so that the target angular displacement corresponds to the belt thickness variation after the phase changes according to the detected belt stop position. The target angular displacement Ref (i) stored in (1) is corrected. If the belt portion stopped at a specific point undergoes a thickness change due to being left unattended, the phase of belt thickness fluctuation may change before and after being left unattended. For example, when a part other than the thickest belt part stops at a specific point and is left to be thickened, and the belt thickness becomes thicker than the thickest belt part, or a part other than the thinnest belt part However, when the belt is stopped at a specific point and left unattended and the thickness of the portion becomes thinner than that of the thinnest belt portion, it can be considered that the phase of belt thickness variation has changed. Since the specific point where the belt becomes thicker or thinner due to neglect is known in advance, if the belt stop position can be ascertained, the amount of phase change before and after neglect can be obtained. Therefore, in the above-described correction example 1, it is possible to obtain a more appropriate target angular displacement Ref (i) by correcting the target angular displacement Ref (i) with respect to the phase based on the belt stop position.
In the above-described correction example 2, when the drive of the belts 60, 224, 301, and 410 is stopped, the drive control system shown in FIG. 4 performs control so that the belt stops at a predetermined reference stop position. Therefore, it is not necessary to detect the belt stop position each time as in the above correction example 1, and the control can be simplified. In particular, the belt 60, 224, 301, 410 is left in the belt circumferential direction before being left at a specific point where the belt thickness is increased by leaving the belt 60, 224, 301, 410 in the driving stop state (in the vicinity of the entrance roller 61 in the first embodiment). If the position at which the thick belt portion stops is the reference stop position, the belt thickness fluctuation phase does not change before and after being left. Therefore, it is not necessary to correct the target angular displacement Ref (i) related to the phase, and a simpler correction process can be realized. Conversely, if the belts 60, 224, 301, and 410 are left in the drive stopped state, the belt circumference before leaving is set at a specific point where the belt thickness increases (in the vicinity of the entrance roller 61 in the first embodiment). If the position at which the thinnest belt portion stops in the direction is set as the reference stop position, the amplitude of the belt thickness fluctuation can be reduced. If the amplitude of the belt thickness variation is reduced, the drive variation range of the drive motor when the additional value control is performed on the target angular displacement Ref (i) is reduced, so that more accurate drive control is possible.
The image forming apparatus according to the first embodiment includes an endless belt that is stretched over a plurality of support rotating bodies, and carries a recording material on the surface and conveys the recording material conveying member as a recording material conveying member. 60. The image forming apparatus also includes toner image forming units 1Y, 1M, 1C, and 1K as image forming units that form an image on transfer paper conveyed by the paper conveying belt 60, and a drive source that generates a rotational driving force. The pulse motor 110 and a drive that controls the pulse motor 110 to transmit the rotational driving force from the pulse motor 110 among the support rollers 61 to 68 that are a plurality of support rotating bodies on which the paper conveyance belt 60 is stretched. Drive control means for controlling the rotation of the drive roller 63 as a support rotator, and the belt drive control device described above is used as the drive control means. In this image forming apparatus, even if the belt thickness at a specific point (in the vicinity of the entrance roller 61) is changed by leaving the paper conveyance belt 60 in the drive stop state, the paper conveyance belt 60 is driven at a constant speed after the change. can do. As a result, it is possible to obtain a high-quality image without color misregistration or image expansion / contraction with respect to the image as it is.
In the image forming apparatuses according to the second, third, and fourth embodiments, the intermediate transfer belt 224, the photosensitive belt 301, and the intermediate transfer belt are used as an image carrier including an endless belt that is stretched over a plurality of support rotating bodies. 410. In addition, these image forming apparatuses control image forming means for forming an image on these belts 224, 301, and 410, a driving source that generates a rotational driving force, and these belts 224 by controlling the driving source. , 301, 410, drive control means for controlling the rotation of a drive roller as a drive support rotator to which a rotational drive force from a drive source is transmitted, among these support rotators, The images on the belts 224, 301, and 410 are finally transferred onto a transfer sheet as a recording material to form an image on the transfer sheet. In these image forming apparatuses, since the belt drive control apparatus described in the first embodiment is used as the drive control means, the belt thickness at a specific point can be increased by leaving these belts 224, 301 and 410 in the drive stop state. Even if it changes, these belts 224, 301, 410 can be driven at a constant speed after being left. As a result, it is possible to obtain a high-quality image without color misregistration or image expansion / contraction with respect to the image as it is.
In the image forming apparatuses according to the first embodiment and the fourth embodiment, the image forming unit forms images of different colors on the photosensitive drums 11 and 418, which are a plurality of latent image carriers, respectively. The images are formed on the transfer paper transported by the paper transport belt 60 or on the intermediate transfer belt 410 so as to overlap each other. Therefore, such a so-called tandem type image forming apparatus has an advantage that the image forming speed is excellent, but extremely high accuracy is required for alignment between the images on the photosensitive drum. Therefore, if the belt thickness changes due to neglect and the belt moving speed is not constant, color misregistration may occur, but such color misregistration can be suppressed by the belt drive control device.

5 is a flowchart showing a control flow in target value data correction example 1 in the laser printer of the first embodiment. FIG. 2 is a schematic configuration diagram of the laser printer. FIG. 2 is an enlarged view showing a schematic configuration of a transfer unit provided in the laser printer. The block diagram which shows the structure of the control system which digitally controls the angular displacement of a pulse motor based on the state detection signal of a drive roller. The drive control block diagram which controls the rotation angle displacement of the drive roller by the pulse motor. The graph which shows the thickness change of the belt part of the vicinity (specific point) of the entrance roller according to leaving time. 9 is a flowchart showing a control flow in correction example 2. FIG. 3 is a schematic configuration diagram illustrating a color copying machine according to a second embodiment. FIG. 5 is a schematic configuration diagram of a color copying machine according to a third embodiment. FIG. 6 is a schematic configuration diagram of a color copying machine according to a fourth embodiment.

Explanation of symbols

1Y, 1M, 1C, 1K Toner image forming unit 11Y, 11M, 11C, 11K, 212 Photosensitive drum 60 Paper transport belt 61 Entrance roller 63 Drive roller 67Y, 67M, 67C, 67K Transfer bias applying member 81 Mark detection sensor 100 Transfer Paper 101 Microcomputer 102 Microprocessor 104 RAM
110 Pulse Motor 111 Encoder 224 Intermediate Transfer Belt 301 Photosensitive Belt 410 Intermediate Transfer Belt

Claims (7)

Target value storage means for storing target value data for canceling fluctuations in belt moving speed due to periodic belt thickness fluctuations in the circumferential direction of an endless belt stretched over a plurality of support rotating bodies;
Rotation control means for controlling the rotation of the drive support rotator to which the rotational drive force is transmitted among the plurality of support rotators based on the target value data stored in the target value storage means;
Stop position detection means for detecting the stop position of the belt when the driving of the belt is stopped;
Time measuring means for measuring a standing time from the stop of driving of the belt to the start of the next driving;
Based on the stop position detected by the stop position detecting means, the belt portion located at a specific point where the thickness of the belt changes is specified by leaving the belt in a driving stop state, and the time measuring means Based on the measurement result, the target value stored in the target value storage means so as to become target value data corresponding to the belt thickness variation after the belt thickness change of the belt portion due to the neglected time for the measurement result. A belt drive control device comprising target value correction means for correcting data. In the belt drive control device according to claim 1,
The target value correcting means stores the target value based on the stop position detected by the stop position detecting means so as to become target value data corresponding to the belt thickness fluctuation after the phase changes according to the stop position. A belt drive control device for correcting target value data stored in the means. In the belt drive control device according to claim 1,
The rotation control means controls the belt so as to stop at a predetermined reference stop position when stopping the driving of the belt. In the belt drive control device according to claim 3,
The reference stop position is a position where the thickest belt portion or the thinnest belt portion stops in the circumferential direction of the belt before being left at a specific point where the belt thickness changes when the belt is left in a drive stop state. A belt drive control device. A recording material conveying member comprising an endless belt stretched around a plurality of support rotating bodies, carrying a recording material on the surface and conveying it;
Image forming means for forming an image on a recording material conveyed by the recording material conveying member;
A drive source that generates rotational driving force;
Drive control means for controlling the drive source to control the rotation of the drive support rotator to which the rotational drive force from the drive source is transmitted among the plurality of support rotators over which the recording material conveying member is stretched; In an image forming apparatus having
An image forming apparatus using the belt drive control device according to claim 1 as the drive control means. An image carrier comprising an endless belt stretched around a plurality of support rotating bodies;
Image forming means for forming an image on the image carrier;
A drive source that generates rotational driving force;
Drive control means for controlling the drive source to control the rotation of the drive support rotator to which the rotational drive force from the drive source is transmitted among the plurality of support rotators over which the image carrier is stretched; Have
In an image forming apparatus for finally transferring an image on the image carrier onto a recording material to form an image on the recording material,
An image forming apparatus using the belt drive control device according to claim 1 as the drive control means. The image forming apparatus according to claim 5 or 6,
The image forming unit forms images of different colors on a plurality of latent image carriers, and the images of the respective colors overlap each other on the image carrier or a recording material conveyed by the recording material conveying member. An image forming apparatus that forms an image as described above.

Images